Battery packs have been known that are configured to accommodate battery cells in a sealed case. In this type of battery pack, the internal pressure of the sealed case needs to be lowered when the internal pressure is high.
Patent Document 1 discloses a battery module that has a housing serving as a sealed case and rechargeable batteries serving as battery cells accommodated in the housing. A gas discharging member, which is opened at a preset pressure, is attached to each rechargeable battery. The housing has a gas discharging hole. A valve member is attached to the housing to close the gas discharging hole. The battery module is configured such that the valve member is opened when the internal pressure of the housing reaches a preset pressure.
In this battery module, when the gas discharging members of the rechargeable batteries are opened, various types of gases are discharged from the gas discharging members. Since the weights of the gases discharged from the gas discharging members differ depending on the types, the distribution of the gases in the housing becomes uneven. Thus, even if the internal pressure of the housing is high and the valve member is opened, some of the various types of gases may remain in the housing.